Abstract
The solid oxide fuel cell (SOFC) nickel-yttria stabilized zirconia (Ni-YSZ) anode degradation due to different types of siloxane contamination is investigated. A cyclic structure siloxane, octamethylcyclotetrasiloxane (D4), and a linear structure siloxane, decamethyltetrasiloxane (L4), are mixed with H2+N2 as the fuel for SOFCs at 750°C. The electrochemical characterization results after stability experiments suggest that the SOFC contaminated with cyclic siloxane, D4, had higher degradation. Pure YSZ pellets with different surface hydroxylation extents were also tested to investigate the D4/L4 adsorption and deposition process. Postmortem SEM/WDS, XRD and Raman analysis all indicate that cyclic siloxane has more deposition than linear siloxane on the anode. Further analysis demonstrates that high adsorption and low desorption rates of cyclic siloxane on YSZ are linked to the degradation. Besides the silicon deposition, SiC and amorphous carbon deposition were also observed from the XRD and Raman analysis.
Highlights
Biogas is generated during the natural degradation of organic material by microorganisms under anaerobic conditions
Based on the solid oxide fuel cell (SOFC) siloxane contamination studies, the experiment with L4 as contamination source had less performance degradation compared with D4
Hydroxyl groups can be formed on YSZ, based on Eqs 4, 5, through reduction of YSZ by hydrogen, which only occurs near the surface, or through reaction with oxygen ions transported through the YSZ (Ong et al, 2016)
Summary
Biogas is generated during the natural degradation of organic material by microorganisms under anaerobic conditions. Wastewater treatment plants utilize the anaerobic digestion process converting organic material in wastewater to biogas. The biogas collected from wastewater treatment plants and landfills is considered a renewable fuel that could be used to produce electricity, heat or as vehicle fuel (Scarlat et al, 2018). Biogas from organic waste digesters usually contains from 60 to 70% methane, from 30 to 40% carbon dioxide and
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